Many low pressure and near depleted oil and gas wells have a low fluid production rate (1-5 m3/day). This complicates cost effective removal of such fluid, including potential damage to a pump due to dry pumping.
Down-hole hydraulic pumps with the valving, piston and pump (and its variations) were originally developed under the trade names “Kobe” and “Oilmaster”. Both have been available to the industry for more than five decades. These pumps find special application lifting large volumes of light oil in deep wells.
More recently, Canadian application 2,258,237 by Cunningham suggested bringing the valving to the surface, and proposed using a downhole double acting hydraulic piston, three (3) strings of tube and a conventional oil well pump for placement in a horizontally drilled heavy oil well. The double acting feature of the hydraulic piston would be particularly useful as a pump pull-down in the highly viscous heavy oil applications for which the system was conceived. Canadian patent 2,260,518, also by Cunningham, proposes using a down-hole rotary hydraulic drive, coupled to a progressing cavity pump rather than the reciprocating version suggested by the earlier Cunningham application. Both address the task of pumping heavy oil in deviated well-bores.
Even more recently, U.S. application 2006/0124298 by Geier teaches a method for dewatering a gas well where the water is pumped to surface by an inverted API pump acting as a reciprocating pump (the entirety of which is incorporated by reference herein). The design of Geier may suffer from a number of disadvantages, including those typically associated with API rod pumps (which are unable to run dry and therefore will require complex control systems to operate in low fluid production rate applications), appears overly complex (requiring additional components such as a counter balance chamber, multiple pistons, a charge of oil between some of the pistons, soft seal packs to prolong pump life and a traveling valve) and requires the use of a modified traveling barrel API sucker rod pump (which adds to the overall expense).
Additionally many fields of shallow gas wells are being produced by scheduled dewatering using service equipment such as blow downs or swabbing. Such traditional methods of dewatering are inefficient and don't maximize well production because, right after such dewatering treatment, the well will begin loading again with water, negatively affecting well production.
For example, swabbing may be scheduled on a weekly basis for a gas well which produces about a cubic meter (m3, i.e. 1000 L) of water per day. Well production will be maximized shortly after swabbing, but then as water builds or loads up in the wellbore, production will decrease to a low level until the next scheduled swabbing event. This cyclic water loading (and associated decrease in production rates) creates inefficiencies in the well's overall production.
What is therefore desired is a novel submersible pump arrangement for use with low rate fluid inflow, which overcomes the limitations and disadvantages of the existing arrangements, which removes wellbore fluids as they accumulate (rather than only at scheduled times), which has a low installation and purchase cost and which will eliminate the need for expensive scheduled dewatering operations such as blow downs or swabbing.